Observation of a Quasi-2-Day Wave during TOGA COARE

Abstract

Detailed structure of the quasi-2-day oscillation observed in the active phase of the Madden?Julian oscillations during the intensive observation period of Tropical Ocean and Global Atmosphere Coupled Ocean?Atmosphere Response Experiment (TOGA COARE IOP) was described. A variety of observational platforms is used including high-resolution GMS infrared histogram, rain-rate estimate from TOGA and MIT radar measurements, upper-air soundings, and boundary layer profiler winds from the Integrated Sounding System and surface data from the IMET buoy. The quasi-2-day mode had a westward propagation speed of 12°?15° day ?1, a horizontal wavelength of 25°?30° longitude. A coupling with the westward-propagating n = 1 inertio?gravity waves was hypothesized from the space?time power spectral distribution of the cloud field. The wind disturbance structure was consistent with the hypothesis. The vertical wave structure had an eastward phase tilt with height below 175 hPa and vice versa above, indicating the wave energy emanating from the upper troposphere. Four stages in the life cycle of the oscillating cloud?circulation system were identified:. 1) the shallow convection stage with a duration time of 12 h, 2) the initial tower stage (9 h), 3) the mature stage (12 h), and 4) the decaying stage (15 h). Surface and boundary layer observations also showed substantial variation associated with the different stages in the life cycle. Results suggest that the timescale of quasi-2-day oscillation is determined by the time required by the lower-tropospheric moisture field to recover from the drying caused by deep convection.